b8c8cb2770
Explicitly mention that IDs effectively used when wxID_ANY is specified as well as IDs returned by NewControlId() are negative and that the user IDs should be positive to avoid clashing with such auto-generated ones.
64 lines
2.9 KiB
C
64 lines
2.9 KiB
C
/////////////////////////////////////////////////////////////////////////////
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// Name: windowids.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_windowids Window IDs
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@tableofcontents
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Various controls and other parts of wxWidgets need an ID. Sometimes the ID may
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be directly provided by the user or have a predefined value, such as
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@c wxID_OPEN. Often, however, the value of the ID is unimportant and in this
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case it is enough to use @c wxID_ANY as the ID of an object which tells
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wxWidgets to assign an ID automatically. All such automatically-assigned IDs
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are negative, so the IDs predefined in the user code should always be positive
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to avoid clashes with them.
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If you do care about the ID value but don't want to specify it as a literal in
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your code, you can use wxWindow::NewControlId() to create an ID that had never
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been returned by this function before and, being also negative, never conflicts
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with any IDs explicitly defined in the program if the advice above is followed.
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@see wxIdManager, wxWindow::NewControlId(), wxWindow::UnreserveControlId()
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@section overview_windowids_type Data Types
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A wxWindowID is just the integer type for a window ID. It should be used
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almost everywhere. To help keep track of the count for the automatically
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generated IDs, a new type, wxWindowIDRef exists, that can take the place of
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wxWindowID where needed. When an ID is first created, it is marked as reserved.
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When assigning it to a wxWindowIDRef, the usage count of the ID is increased,
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or set to 1 if it is currently reserved. Assigning the same ID to several
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wxWindowIDRefs will keep track of the count. As the wxWindowIDRef gets
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destroyed or its value changes, it will decrease the count of the used ID. When
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there are no more wxWindowIDRef types with the created ID, the ID is considered
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free and can then be used again by wxWindow::NewControlId.
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If a created ID is not assigned to a wxWindowIDRef, then it remains reserved
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until it is unreserved manually with wxWindow::UnreserveControlId. However, if
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it is assigned to a wxWindowIDRef, then it will be unreserved automatically and
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will be considered free when the count is 0, and should NOT be manually
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unreserved.
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wxWindowIDRef can store both automatic IDs from wxWindow::NewControlId and
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normal IDs. Reference counting is only done for the automatic IDs. Also,
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wxWindowIDRef has conversion operators that allow it to be treated just like a
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wxWindowID.
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@section overview_windowids_using Using wxWindowIDRef
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A wxWindowIDRef should be used in place of a wxWindowID where you want to make
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sure the ID is not created again by wxWindow::NewControlId at least until the
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wxWindowIDRef is destroyed, usually when the associated object is destroyed.
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This is done already for windows, menu items, and tool bar items. It should
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only be used in the main thread, as it is not thread safe.
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*/
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